Traditional channel-based digital audio coding systems mix all audio content such as dialogue, background music, and sound effects into one or more channels of information and encode those channels into a digital bitstream. This digital bitstream may be generated remotely and delivered to a user's playback system by broadcasting, point-to-point transmission on a network or recording onto a storage media for later retrieval, or may be generated locally for immediate rendering and playback such as by a video game. The audio content of each channel is intended to be reproduced by one or more loudspeakers during playback according to the number and arrangement of the loudspeakers in the playback environment.
After audio content is mixed and encoded into a digital bitstream by a channel-based digital audio coding system, removing audio elements or adding audio elements to the digital bitstream requires an additional decoding of the encoded bitstream, which requires additional computational resources and increases implementation costs of devices. For some systems, the decoded bitstream must be encoded again, which further increases implementation costs.
The additional complexity needed to add or remove audio elements is disadvantageous in audio playback systems incorporating devices such as Blu-ray players, broadcast set-top boxes and game consoles that provide additional or supplementary audio content intended to be played back with the principal audio content of an encoded digital bitstream. For example, some devices generate audible feedback for operations performed by a user to select playback options, play a video game or provide audio content associated with a picture shown within another picture. Some applications offer interactive or live audio content such as multi-player gaming applications that offer the ability for a player to “chat” with other remotely-located players during game play, or applications that generate audio alerts to notify a user of an event such as the arrival of a message.
Traditional channel-based audio playback systems cannot easily reproduce both the principal audio content and the supplementary audio content as described above because the traditional devices in these systems cannot easily combine their supplementary audio content with the principal audio content of an encoded digital bitstream that is being reproduced or played back by the audio system.
Another coding technique known as spatial audio object coding has been introduced within the past few years. Proposed audio object-based coding techniques promise some improvements over channel-based techniques but more improvement is still needed.